Processes for the base-catalyzed preparation of organopolysiloxane resins and organopolysiloxane elastomers are already known. For example, EP-B-42 208 describes a process for the preparation of organopolysiloxane resins, involving the metered addition of alkoxysilane and hexamethyldisilazane to a mixture of water and alcohol. The use of different quantities of water and the choice of the ratio of the molar fractions of monofunctional units to tetrafunctional units in this case enables the molecular weight of the resins to be controlled.
One possibility for the preparation of graft copolymers comprises grafting a polymer carrying a reactive, functional end group with reactive monomers. This is called a "grafting onto" process. For example, in EP-A-539 901 vinyl monomers are grafted by emulsion polymerization onto an emulsified organopolysiloxane which contains attachment sites. The attachment sites are produced by dialkoxysilanes which are incorporated into the organopolysiloxane by condensation and contain a radical-forming group. In this "grafting onto" process an external redox initiator system is used to initiate homopolymerization of the organic monomers, the growing organopolymer chains becoming attached in this case to the attachment sites of the organopolysiloxane graft backbone. A disadvantage of this process is that the attachment of the organopolymer to the polysiloxane is not a matter of course, and thus a considerable portion of the organopolymer is not grafted onto the polysiloxane but is present as an unattached homopolymer. A further disadvantage of the "grafting onto" process is that, as a result of intramolecular linkages, especially the formation of loops by multiple attachment of the organopolymer chain to the organosilicon polymer core, graft copolymers of uncontrolled composition are formed, a fact which can be demonstrated by structural characterization of such graft copolymers, for example using static and dynamic light scattering.
The object was to provide organopolysiloxane resins and organopolysiloxane elastomers which have radical-forming groups, can be prepared with simplicity and a high degree of reproducibility, and can be used to synthesize, by free-radical polymerization, graft copolymers which do not have the above mentioned disadvantages of the known graft copolymers, namely a high proportion of organopolymer homopolymer and an uncontrolled composition.